Temperature responsive switching apparatus, known commonly as cold controls, are used for refrigeration appliances, such as freezers and the like, to control the temperatures therein. These cold controls are customarily regulated by a switch which cycles a compressor on and off in response to the measurement of the temperature of the air contained at some point in the appliance by a temperature sensing means. When the temperature exceeds a certain point, the compressor is switched on to cool the appliance. When the temperature of the appliance has been cooled past to a particular value, the compressor switches off until the cycle begins again when the temperature rises.
One problem with the control of the temperature of refrigeration appliances, particularly freezers, using cold controls is that there is no facile way of determining there has been a failure if a portion of the control system fails. Such appliances are kept closed and are automatic in their operation for long periods of time. Because they are unattended and unobtrusive in their operation, the cold control, the compressor, or other system components may fail and the contents of a freezer become defrosted before anyone is alerted to the situation. With freezers of the commercial variety this can be especially detrimental because of their large capacity. Many foodstuffs which are stored in commercial freezers must be disposed of once they have been thawed and cannot be refrozen.
To alleviate this problem, some in the art have proposed alarm systems to warn when a freezer has quit operating. For example, Rossi, et al. in U.S. Pat. No. 4,510,480 and GB application No. 2,11l,203A describe auxiliary and warning switches used in conjunction with a cycling control switch for refrigeration appliances. Andresen in U.S. Pat. No. 3,735,069 further describes a fault indicator switch used in conjunction with a thermostatic control having a snap-action switch.
These alarm systems must work in concert with the cold controls to cycle the apparatus back and forth between the operating temperatures but must also sense when the appliance has stopped working properly. Such alarm systems should be inexpensive to add to cold controls and should be readily integrated into such controls without major changes in control philosophy or structure. They should also exhibit robustness and reliability in operation. Another important criterion is the ability to interface with other cold control features, such as defrost cycles without producing false alarms.
One popular cold control contains a U-shaped snap-acting spring which is used in the compressor cycling portion of the control. This control is highly advantageous in that it is simple and reliable because the snap action provides a sure switching action which is dependable for many cycles of the control. The control is also very robust because of the high energy content of the switching action which, once the spring constant of the U-shaped spring has been overcome, snaps the switch operator from a first position to a second position or back. The energy of the snap-action is absorbed by stationary stops at the two extreme positions. While making the switching action very sure, the energy absorbing stops do cause difficulties in designing additional features for the cold control. They limit movement and therefore, temperature based force generation and actuation beyond these two positions by the switch operator.
Examples of this general type of control are disclosed in U.S. Pat. No. 3,065,323 issued to C. Grimshaw, U.S. Pat. No. 3,065,320 issued to R. W. Cobean, U.S. Pat. No. 3,096,419 issued to L. J. Howell, U.S. Pat. No. 3,354,280 issued to J. L. Slonneger, U.S. Pat. No. 3,648,214 issued to J. L. Slonneger, and U.S. Pat. No. 4,490,708 issued to Thompson, et al. All of these patents are assigned to the General Electric Company, the assignee of the present invention, and their disclosure is hereby expressly incorporated herein by reference.
It would be to great advantage to provide a cold control with a snap-action switch including an alarm feature which could be integrated into the switching mechanism without changing the advantages and control philosophy of the snap-action of the apparatus.